The present invention relates generally to hand-held optical scanners and, more particularly, to hand-held optical scanners in which the speed of hand scanning is controlled through the use of tactile feedback to the operator.
Optical scanners are used to produce machine-readable data which is representative of a scanned object, e.g. a page of printed text. Optical scanners employ line-focus systems to image scanned objects.
In a line-focus system, a light beam from an illuminated line object is imaged by a lens on a linear photosensor array which is positioned remotely from the line object. In an optical scanning device, the illuminated line object of the line-focus system is commonly referred to as a "scan line". The linear photosensor array is a single dimension array of photoelements which correspond to small area locations along the line object. These small area locations on the line object are commonly referred to as "picture elements" or "pixels". In response to light from its corresponding pixel location on the line object, each photoelement produces a data signal which is representative of the intensity of light which is impinged upon it. All of the photoelement data signals are received and processed by an appropriate data processing system which may subsequently store the data on a suitable medium or generate a display signal therefrom for reproducing an image of the object with a display device such as a CRT or printer.
Optical scanners and various components thereof are disclosed in U.S. Pat. No. 4,926,041 for OPTICAL SCANNER of David Wayne Boyd; U.S. Pat. No. 4,709,144 for COLOR IMAGER UTILIZING NOVEL TRICHROMATIC BEAM SPLITTER AND PHOTOSENSOR of Kent J. Vincent; and U.S. Pat. No. 4,870,268 for COLOR COMBINER AND SEPARATOR AND IMPLEMENTATIONS of Kent J. Vincent and Hans D. Neuman, which are each hereby specifically incorporated by reference for all that is disclosed therein.
Most optical scanners have photoelectric conversion assemblies which employ charge coupled device (CCD) type photosensors. All of the photoelements in a CCD linear array have the same fixed operating (sampling) interval, e.g. one millisecond. A data signal is produced by each element at the end of an operating interval and is representative of an average of the light intensity which the element experiences during the operating interval. The scan speed of a scanner employing a linear CCD photosensor array is thus limited by the CCD operating interval. If the scanner displacement rate is greater than one scan line width per CCD operating interval, the scanner will not be able to collect enough data to produce an accurate representation of the document which is being scanned. In most types of optical scanners, e.g. flatbed, sheet-fed and overhead scanners, the scan speed is directly controlled by the scanner control system. The control systems of such scanners are typically designed to provide a scan speed which is less than, but near the maximum scan speed possible for proper operation with the system photoelectric conversion assembly.
A hand-held optical scanner is an optical scanner which is moved across a scanned object, e.g. a page of text, by hand. During hand scanning, the scanning speed, i.e., the speed at which an operator moves the scanner across the object, is dependent on the operator. If an operator moves the scanner too rapidly with respect to the operating speed of the scanner photoelectric conversion assembly, data necessary for creating an accurate image of the scanned object will be lost. On the other hand, if the operator moves the scanner at a low rate of speed to avoid data loss, the scanning process may take much more time than is necessary.
U.S. Pat. No. 4,703,186 of Nakayama et al., which is hereby specifically incorporated by reference for all that it discloses, describes a hand-held optical scanner with a speed control device. Several different speed control embodiments are described. In one embodiment, a friction disk is mechanically linked to a guide roller which rotates as the scanner is moved across a document. The friction disk is constructed to expand and move into frictional contact with a housing and thus produce a load resisting scanning motion when scanning speed exceeds a predetermined speed. In another embodiment, a flywheel and a rotating weight which moves radially outwardly relative to its rotation axis with increased scanning speed is employed to limit scanning speed and maintain a relatively smooth scanning speed. In another embodiment, the scanning unit is moved along a guide rail. An associated guide roller rotates, and thereby a DC motor is rotated in the reverse direction. "Then, the DC motor functions as a generator which produces a load practically proportional to the revolving rate thereof. The load thus produced tends to maintain the revolving rate of the guide roller at a fixed value, which controls the moving speed of the scanning unit for an approximate uniform motion."
Nakayama et al. thus describes certain methods for limiting scanning speed, but does not consider the performance problem associated with scanning at a speed slower than necessary.